In a checkout system for retailers, a registration device generates accounting data required for settlement of a transaction. The registration device is separated from a settlement device performing a settlement process of the transaction on the basis of the accounting data. The registration device waits for input of data related to commodity sales. If data related to commodity sales is input by an operator, the registration device generates accounting data on the basis of the input data, and transmits the accounting data to the settlement device. The settlement device waits for input of payment data with respect to the accounting data. If payment data is input by the operator, the settlement device performs a settlement process of the transaction on the basis of the accounting data and the payment data. A checkout system in which a registration device is separated from a settlement device may be a two-person system in which different salespersons respectively operate the registration device and the settlement device. Alternatively, the checkout system may be a sharing system or a so-called semi-self-service system in which a salesperson operates the registration device, and a shopper operates the settlement device.
In the semi-self-service system, accounting data for a settlement process is transmitted from a registration device to an available settlement device. Thus, if all settlement devices are performing settlement processes, accounting data cannot be transmitted to one of the settlement devices. If accounting data is transmitted to a settlement device in which an error such as receipt sheet shortage or abnormality in a change machine has occurred, a settlement process cannot be performed. Thus, the accounting data must be retransmitted to another settlement device. In this case, a purchase registration process in a registration device is delayed. Accordingly, it is desirable to efficiently perform processes for purchase registration and settlement.